Aircraft: WIDEBODY TRANSPORT
Phase of flight: Initial Approach; Descent
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Speed All Types

Low speed event at 6000 feet during approach control issued short notice level off with speed brakes extended; Flaps 5.- Speed brake extended for descent due to tight revised ATC issued short turn to final- Level off issued within a few hundred feet of 6000 feet requiring rapid change to Alt Hold. Speed brakes remained extended during rapid level off precipitating slow speed event- Multiple approach changes issued close in; requiring Captain (CA) to be heads down- RNAV was refused when it was identified as an RNAV-RNP which we are prohibited from executing- FMC locked up twice during vectors to final displaying 'Standby One' for 5-10 sec with previous indications of FMC data corruption earlier en-route requiring close monitoring of FMC- Poor ATC transmitter quality and language barrier requiring numerous clarifications from us by other carriers. ATC was task saturated rushing the pattern- After slow speed event I took control of the aircraft; declared missed approach; stabilized the aircraft on downwind; reduced automation level to basics and turned aircraft back over to First Officer (FO) for a visual approach and landing- FO is new to aircraft; very low time in FO seat; and mostly assigned FB position since qualified; coming from MD80- FB was heads down during event pulling up continuously changing approaches issued by approach controlCONTRIBUTING FACTORS- Little to no sleep due to continuous turbulence at lower altitudes during breaks resulting in being awake for 24hrs.Carriers may be following the letter of the law; complying with crew rest FARs; FAA training requirements; and union contract limitations to stay legal and compliant. But carriers and the FAA collectively fail to get out from among the trees and step back and look at the forest; or big picture.Safety is severely compromised when pilots are rushed through a fast paced course into a new; highly complex; and automation intensive aircraft; transitioning from steam gauges and cables; then relegating them to the back seat (FB) to 'watch' without 'doing' for years. Add to this an occasional assignment on reserve to the FO seat; place them in a situation of severe sleep deprivation that equates to being legally drunk; send them to arguably the most demanding environment in the international system with malfunctioning automation; turbulence; and where ATC issues clearance changes that would make a sim check feel like kindergarten; and you have the making of a forest fire. These are serious safety issues; they continue to exist; and speak to core issues which all the human factors classes and new FARs are not addressing.Avoiding this type of event; and others like it; requires policy changes. No amount of human factors pie charts; graphs or pep talks will change that the underlying premise that no one wants to step back and look at the big picture issues because changes will likely cost money.My suggestion; for starters; is to have newly qualified FOs (especially from the MD80) be assigned high density domestic legs for one or two months before going international and being relegated to the FB seat for years. We restrict CA's to 100 hours in the seat before becoming unrestricted. Does an FO not have the same learning curve? [Report narrative contained no additional information.] During descent aircraft experienced a low speed event due to deployed speed brakes during level off. There were multiple changes in the approach by ATC increasing the crew workload. A missed approach was executed. The FMS was at times slow to respond to changes.